1. Field of the Invention
This invention relates, generally, to coating compositions. In particular, the compositions of the present invention are used to coat bulk solids. These coating compositions contain a bituminous material and an effective amount of a methyl/ethyl ester diluent. The compositions of the present invention are particularly suited to reduce dust formation and cake formation in fertilizers.
2. Description of the Related Art
The storage and handling of bulk materials present unique problems relating to both dust formation and cake formation. Specifically, dust formation and dissemination pose safety, health and environmental problems. Cake formation presents problems in storing and handling of bulk materials.
These problems are particularly problematic in the fertilizer industry. Specifically, fertilizers, which are generally in powder, crystalline or granular forms have a tendency to cake. Over time fertilizers form more or less solid masses due to changes in humidity and/or temperature. Prior to application the fertilizer must be broken up to provide a material that is suitable for even distribution in the field and to prevent clogging of distribution machinery.
Fertilizer dust consists of fertilizer particles that are small and light enough to become airborne. Excessive dust is problematic for both producers and end-users. Specifically, fertilizer dust creates numerous problems, including, problems associated with environmental compliance, worker safety, worker productivity and increased maintenance and repair of handling and storage equipment. In addition, dust levels tend to increase over time and are aggravated by prolonged storage and storage at less than ideal conditions. Further, fertilizer dust poses a problem of spontaneous combustion. Spontaneous combustion is problematic because it relates to both the processing temperature of fertilizers as well as and the storage temperature of the finished fertilizer products.
Various approaches have been developed to overcome the problems associated with fertilizer caking and dusting, some with a measure of success. For example, fertilizer granulation by agitation with a small amount of water at elevated temperature, mixing fertilizers with inert mineral materials or bulky organic materials, spraying the fertilizer with molten materials, such as, paraffin waxes, asphalts and petroleum resins, to form pellets of uniform size and reduce the points of contact between fertilizer particles have been found to inhibit caking and reduce dust formation for brief periods of time. Other approaches for the reduction of caking and dusting include shipping fertilizers in moisture proof bags or other containers and growing large crystals which are screened to uniform sizes.
Asphalts have been particularly useful in coating fertilizers. In order to produce an asphalt based coating agent it is necessary to reduce the viscosity of the asphalt so that it can be sprayed onto the fertilizer. Traditionally petroleum based oils have been used for this purpose.
Methyl and ethyl esters of fatty acids are well known and find application in many areas, including as a carrier for herbicides in the agricultural area and as a solvent for cleaning equipment used in the asphalt industry.
Some of the treatments described above which are used to improve anti-caking in fact produce dusting problems. In addition, although these additives and treatments may show improved anti-caking and anti-dusting properties, they all reduce the concentration of the nutrients in the fertilizer, resulting in a lower grade product. Further, impregnating or coating the fertilizer particles interferes with the rate of release of nutrients.
Based on the foregoing, asphalts have been used to coat fertilizers and methyl/ethyl esters have been used as carriers for herbicides and solvents for cleaning equipment in the asphalt industry. There has been no suggestion whatsoever, however, that fertilizers coated with asphalts containing methyl/ethyl esters would exhibit superior anti-caking and anti-dusting properties. Accordingly, in view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the needed fertilizers having improved dust control and reduced caking properties, could be provided, without adversely impacting the quality and/or rate of release of the fertilizer.
In accordance with the present invention, a composition for coating bulk solids is provided. The bulk solids of the present invention include organic materials, inorganic materials and combinations thereof which are granulated, crushed, compacted, crystalline or prilled solids and combinations thereof. The coating contains a bituminous material and an effective amount of an ester diluent. Bituminous materials useful in the present invention include asphalt, asphaltic tars, asphaltic pitches, coal tars, coal pitches and combinations thereof. The ester diluent is a methyl or ethyl ester of fatty acids, oils and combinations thereof derived from animal, plant and synthetic materials. The effective amount of the ester diluent is from about 0.01% to about 99.9% by weight of the total weight of the coating composition.
The viscosity of the coating composition is from about 3 cP to about 20000 cP, preferrably 3cP to about 5000 cP, at 60xc2x0 C. Specifically, the coating compositions useful in the present invention have viscosities, which are less than viscosities of coating compositions containing an effective amount of a petroleum hydrocarbon diluent. More particularly, the viscosity of the coating composition of the present invention is less than that of a coating composition which contains a petroleum hydrocarbon diluent in an amount of from about 0.01% to about 99.9% by weight of the total weight of the coating composition.
Bulk solids coated with these inventive coating compositions generate less dust than those coated with coating compositions containing an effective amount of a petroleum hydrocarbon diluent. Specifically, bulk solids coated with the present coating compositions generate less dust than bulk solids coated with a coating composition containing a petroleum hydrocarbon diluent in an amount of from 0.01% to about 99.9% by weight of the total weight of the coating composition. In addition, bulk solids coated with the coating composition of the present invention cake less than bulk solids coated with a coating composition containing an effective amount of a petroleum hydrocarbon diluent. In fact, bulk solids coated with the coating composition of the present invention cake less than bulk solids coated with a coating composition containing a petroleum hydrocarbon diluent in an amount of from about 0.01% to about 99.9% by weight of the total weight of the coating composition.
The invention accordingly comprises the features, and combination of elements in the following description, and its scope, will be pointed out in the appended claims.
The present invention relates to coating compositions for bulk solids containing bituminous materials and methyl esters and/or ethyl esters. Preferably these coatings are used to treat fertilizers to reduce both cake and dust formation. Specifically, it has been found that methyl or ethyl ester diluents advantageously replace prior art petroleum based oil diluents to provide a superior sprayable asphalt coating composition.
In particular, the amount of ester diluent required to achieve a sprayable asphalt composition is considerably less than the amount of petroleum based oil diluent required, resulting in more asphalt at the surface of the fertilizer granule, and hence providing a superior anti-dusting and anti-caking effect. In addition, the flash point of methyl/ethyl esters is greater than that of petroleum based oil diluents resulting in a safer, less combustible, less flammable coating material.
Bituminous materials useful in the present invention include asphalt, asphaltic tars, asphaltic pitches, coal tars, coal pitches and combinations thereof. These bituminous materials are available in a number of grades and from a number of sources. For example, bituminous materials, and asphalt in particular, may be obtained from Marathon Oil Company, Tampa, Fla., The Coastal Corporation, Port Canaveral, Fla. and Mariani Asphalt, Tampa, Fla.
The methyl and/or ethyl esters useful in the present invention can be distilled, following reaction with an appropriate alcohol, by methods known in the art, from various sources including, but not limited to rapeseed oil, sunflower oil, corn oil, safflower oil and soybean oil. The esters useful in the present invention are chains of from 8 to 24 carbon atoms, with the following general formula 
wherein n=6xe2x88x9222 and R is CH3 or CH2CH3. Alternatively, these methyl/ethyl esters may be obtained from Ocean Air Environmental, 1248 George Jenkins Boulevard, Lakeland, Fla. 33801. Methyl esters are the preferred diluents.
The coating compositions are used to coat organic and inorganic fertilizer compositions, as well as combinations thereof. The fertilizer, useful in the present invention, is in a granular, pelletized, crushed, compacted, crystalline or prilled form. Fertilizers may be obtained from numerous sources including Cargill Fertilizer, Bartow, Fla.
The coating compositions of the present invention do not interfere with the quality grade or rate of release of the fertilizer. In particular, the coating compositions of the present invention contain an effective amount of a methyl and/or ethyl ester, which is sufficient to dilute the bituminous material to provide a coating material having a viscosity that is suitable for spraying and even distribution on the bulk solids to reduce dust and cake formation while maintaining the quality and nutrient release rate of the fertilizer. The coating composition of the present invention changes the surface characteristics of the bulk solid, rendering it resistant to caking and dusting during shipment and storage.